Guinea pigs, like most small animals, have extremely fast metabolisms. That necessitates a constant supply of food to fuel their bodies. In general, guinea pigs should not go without food for more than 12 hours. It's important to understand that while they might survive for 24 to 48 hours without food, being food-deprived during that period would be extremely stressful for them physically and mentally, and could lead to serious health problems.
Guinea pigs have a unique digestive system that requires a constant supply of food, particularly high-quality hay which helps in their digestion and provides them with necessary fiber. The process of gnawing on hay also helps keep their constantly-growing teeth at a manageable length. If a guinea pig goes without food, it can lead to gastrointestinal stasis (a slowdown or stop of the normal movements of the gastrointestinal tract) that can quickly become a life-threatening condition.
Moreover, they also require intake of Vitamin C daily as their bodies are unable to produce it naturally. They normally get sufficient amounts of Vitamin C from their daily diet of fruits, vegetables, and guinea pig nuggets. A deficiency in Vitamin C can cause scurvy.
Going without food for an extended period can also cause a guinea pig's body to break down its own fat and protein for sustenance. This not only causes substantial weight loss, but can also lead to further complications, such as hepatic lipidosis, or fatty liver disease. The process of liver cells being replaced by fat could end up causing serious damage to the liver, potentially leading to liver failure.
Furthermore, guinea pigs need their feeding schedules to be regular and consistent. Sudden changes to their diet or feeding schedule can cause stress, leading to a weakened immune system and an increased susceptibility to diseases.
If your guinea pig hasn't been eating for more than 12 hours, it's a red flag and you need to seek veterinary help immediately. The cause could be anything from dental disease (guinea pigs can get overgrown teeth that may make eating painful) to various infections or other diseases.
In conclusion, while these small creatures might survive a day or two without food, they should always have constant access to fresh, high-quality food, and clean water. Their health can deteriorate quickly if they're not eating or are underfed. If you notice any changes in your pet's eating habits, seek professional help right away.